An IGBT includes a source region of a first conductivity type (doping type) and a drain region of a second conductivity type complementary to the first conductivity type. The source region is often referred to as first emitter region and the drain region is often referred to as second emitter region. A body region of the second conductivity type adjoins the first emitter region, and a drift region of the first conductivity type adjoins the body region and is arranged between the body region and the second emitter region. A gate electrode is located adjacent the body region, dielectrically insulated from the body region by a gate dielectric, and serves to control a conducting channel in the body region.
In an on-state of the IGBT, the first emitter region injects first type charge carriers via the conducting channel into the drift region and the second emitter region injects second type charge carriers into the drift region where the first type charge carriers and the second type charge carriers form a charge carrier plasma.
Important operation parameters of an IGBT are the saturation voltage (often referred to as VcCEsat) and the saturation current (often referred to as ICEsat). The saturation voltage is the voltage between the first emitter region and the second emitter region of the IGBT at a typical current (rated current) in a normal operation mode of the IGBT. The saturation voltage characterizes the power losses that occur in a normal operation mode of the IGBT. The saturation current is the current that occurs at voltages much higher than the saturation voltage, that is, the saturation current characterizes the behaviour of the IGBT in an overload scenario such as, for example, a short-circuit in a load connected to the IGBT. The critical saturation current, inter alia, defines the robustness of the IGBT against high currents. The higher the critical saturation current the more robust the IGBT is against a current crowding during a short-circuit event.
The critical current can be increased by increasing a doping concentration of the second emitter. Increasing this doping concentration, however, may result in increased losses (that are often referred to as reverse recovery losses) when switching off the IGBT, and higher leakage currents when the IGBT is in the off-state.
There is therefore a need to provide an IGBT with a high critical saturation current and low switching and leakage losses.